My overall objective is to determine the molecular mechanisms by which the contractile proteins of human blood platelets generate force and motion and how these mechanisms are controlled. I plan to study the actomyosin interaction and determine how the different forms of platelet actin and phosphorylated and non-phosphorylated forms of platelet myosin affect this interaction. I would also attempt to elucidate the effects of various platelet activators and inhibitors, especially the prostaglandins and cyclic nucleotides, on the actomyosin interaction. The principal new information to be obtained in this research is the characterization of platelet actomyosin in terms of force-velocity variables measured in a reconstituted thread system which has been recently used to characterize muscular contractile proteins. Correlative data will also be obtained from standard biochemical assays of the actomyosin interaction including ATPase activity, rate of superprecipitation and binding affinity. This would represent the first such analysis not only for platelet actomyosin in particular but also for nonmuscle actomyosin in general. As such, it would permit the first comparisons of the physiological variables of force and velocity between muscle and nonmuscle contractile systems. This information should lead to a greater understanding of the platelet release reaction, platelet aggregation and clot retraction which are dependent on platelet contractile proteins. It should also lead to a greater understanding of pinocytosis, phagocytosis, cellular secretion, contact inhibition, cellular motility, pseudopod formation, chromosomal movement and cytokinesis the cellular processes which depend on actomyosin to transduce the energy of ATP to useful work.